Neurons within the dorsomedial region of the nucleus of the tractus solitarius (mNTS) are essential to the baroreflex, which provides rapid dynamic regulation of the cardiovascular system within a single heartbeat. The objectives of this research are to investigate the intrinsic firing properties and signal processing characteristics of the individual neurons and synaptic interconnections which constitute this medullary cardiovascular control circuitry. Adult rat brainstem will be sectioned at an angle which preserves the mNTS, providing a maximum length of the solitary tract, and will be partially submerged in a perfusion chamber for superfusion of the slice. The research investigations will determine: 1) the effects of known Ca2+-activated K+ current (l KCa) blockers on the repetitive firing characteristics of mNTS neurons, 2) the manner in which the ongoing and evoked patterns of activity in mNTS neurons are influenced by the dynamic interaction between intracellular Ca2+ and lKCa, and 3) the effects of the relative strength of lKCa, (as altered using partial pharmacological block) upon the entrainment and phase-response properties of these spontaneously oscillating mNTS neurons. It is anticipated that these results will enhance our understanding of both the functional properties of mNTS neurons and the biophysical mechanisms contributing in the processing of baroreceptor inputs to this medullary cardiovascular circuitry. Furthermore, these results could potentially reveal new insights into the neurogenesis of such clinical issues as hypertension and cardiac dysrhythmias.